Users of a test and measurement instrument, such as an oscilloscope, often use a probe to connect a device-under-test (DUT), such as a circuit board, to an input of the test and measurement instrument in order to visualize, debug, and perform measurements of electrical signals occurring in the DUT. To measure an electrical signal in a DUT, a user typically needs to establish physical contact between the probe and one or more test points of interest in the DUT. Test points may be located in various places on a DUT circuit board and may be traces or vias, connector pins, or component pads or pins, such as the pins of an integrated circuit (IC). Physically probing a DUT test point can be challenging, especially when the electrical components are very small, or when there are a large number of components packed into a small area. In these cases, the test points of interest can be difficult to access since they may be obscured by other components, cables, or mechanical features of the DUT.
Furthermore, the signals that a probe user needs to measure and debug often operate at high frequencies and low signal levels. For example, high-speed serial busses such as DDR2, DDR4, and PCI Gen 4, among others, are very prevalent in contemporary DUTs. These types of bus signals can have fast rise times, small voltage swings, and high pulse frequencies. Therefore, the test and measurement instruments and probes that are used to measure these types of signals must be high performance, precision devices capable of high bandwidth signal acquisition and good signal fidelity. In particular, the probe should have specified electrical characteristics and performance, and should maintain that specified performance in all use cases.
Sometimes the probe user may need to make physical contact simultaneously with more than one point in a DUT circuit. For example, when measuring a single-ended signal, the user may need to contact the probe to both a test point, as well as to a ground point in the DUT. Or, if measuring a differential signal, the user may need to contact the probe to two test points, where the differential signal is the difference in voltages at the two test points over time. Such pairs of test points may have various amounts of space between them. In order to accommodate variable test point spacing, many probes have adjustment features which allow the distance between the test point contacts on the probe to be changed as necessary. Adjusting these types of probes typically includes adjusting the position of a part of the probe in which the measured signal is conveyed. When a part of the probe in the signal path changes positions, this generally tends to change an electrical characteristic of the probe, potentially to the extent that the probe no longer performs within its specifications. This in turn can lead to an inaccurate measurement of the signal in the DUT. However, conventional adjustable probes are not able to compensate for such electrical characteristic changes to return the performance of the probe to within specification.
Embodiments of the invention addresses these and other limitations of the prior art.